Wireless-telegraph receiving apparatus



0 t. 18 192 E c 7 R. A. WEAGANT WIRELESS TELEGRAPH RECEIVING APPARATUS Original Filed Avril 14. 1920 2 Sheets-Sheet 1 v a, E 7 MT anw/wtoo 33kt W at Oct; 18!

R. A. WEAGANT wmswss TELEGRAPH nscmvme APPARATUS Original Filed April 14. 1 2 2 Sheets-Sheet Patented 0a. 1s, 1927. 1

UNITED. STATES PATENT OFFICE.

BOY A. WEAGANT, OF NEW YORK, N. Y., A S SIGNOR TO RADIO CORPORATION AMERICA, A CORPORATION OF DELAWARE.

WIRELESS-TELEGRAPH RECEIVING PrARAT s.

Application filed April 14, 1920, Serial No'. 373,929. Renewed A ril 1, 1927;

It is well known in the art of wireless telegraphy that transmission by continuous waves is preferable to transmission by damped waves. It is also known that the nearer the continuous wave approaches a sine Wave the better it will carry, especially in long distance transmission. For this reason wireless or radio signals should be propagated to the point of reception without alteration of the sinusoidal character. The frequencies of the propagated waves in practical use, however, are much too high to operate the diaphragm of a telephone receiver and even if this could be done the pitch would be too high to be audible to the human ear. In view of this it is neces sary to so alter or.modulate the continuous wave at the point of reception, that the telephone receiver will produce an audible note, or in some other way render the signal perceptible. This enables the operator to clearly hear or otherwise perceive the dots and dashes, for instance, of the message that has travelled throughout the entire distance in the form of sine waves, except for what modification may have been produced by the medium through which the waves are propagated.

There are known methods of modulation of continuous waves for reception purposes but I have devised further means and methods of accomplishing the desired results and in an entirely novel manner, as far as I am aware.

It can be shown both mathematically and experimentally that iftwo frequencies n and n be applied to the in-put-side of an electron relay such as a three element vacuum tube, for instance, so as to cause a'flow of current in the in-put circuit, there can'be developed in the out-put or plate circuit of the valve a current having components of frequencies n+n and n-n'. If this plate current in turn be applied to the in-put side of a similar valve the out-put current will have components with frequency (n+n) (a -1i) and (Wt-a)-(aan), or 2a and 2% respectively. It is in accordance with this phenomena that I produced the "novel results referred to.

Briefly, my invention consists in'receiving' is either-"an audible frequency or' an inau- 1 dible frequency modulated to secure the results desired. These two frequencies then result in the otherv frequencies in the plate (fll'CUllL as already described. Since the local frequency is an audible one, or isa modulatedhigh frequency, at least one of the plate current frequencies will be audible in the receiving device. With this general description of my invention specific embodiments will now be described to render clear the manner in which the improvement may be carried out.

Referring to the drawings:

Fig. 1 isa circuit diagram for the reception of tion. A

Fig. 2 is a modification.

Fig. 3 is a further modification of the embodiment shown in Fig. 2.

Fig. 4 is an additional modification. v

In Fig. 1 of the drawings a grounded antenna shown conventionally at 1 contains a variable capacity 2 and the primary 3 of a transformer. One terminal of the secondary 4 of this transformer is connected to a grid 5 of a three element valve (shown diagrammatically) and the other to the filament 6 which is heated by some local source waves in accordance with my inven-' "such as a battery 7 A con-denser 9 may also be placed in the lead connected to the grid 5. The connection to the filament 6 includes means for superimposing a local F.

' in the input circuit such as a secondary 8 of a transformer, the 1 primary of which is connected to a generator 10 or other source of alternating current having an audible frequency 500 for example.

The grid should, for best working, be kept negative and this may be accomplished by putting the condenser 9 in the circuit with a grid leak 9' therearound. The same result could be accomplished by putting a battery in this circuit with the negative terminal connected to the grid as shown'in Fig. 2 at 10'.

The plate 11 isljoined to the filament 6 through the battery 12 and primary 13 of a transformer whose secondary 14 is connected to the grid 15 and filament 16 of a second three element valve. The plate 17 of this valve is joined to the filament 16 through the battery 18 and telephone receiver 19 or the like. I

In both of the valves described above, the variable capacities 2O and 21 are connected across the transformer primaries in well known ways.

The operation of the embodiment shown in Fig. 1 is as follows:

The incoming signal induces an E. M. F. of frequency at in the antenna which frequency may be too high to be .audible in a receiving circuit. An E. M. F. of frequency 7 is induced in the secondary 4: and on this is superimposed a; local E. M. F. of audible .frequencyn by means of the local source described. The current produced by these combined E. M. Fs in the plate circuit of the first valve has components (n+n') and .(nfn), The transformer 13, 14 introduces an E. M. F. inthein-put circuit of the second valve that causes a flow of current havingtwocomponents (n+n') (n-n') and (at a) (vi-92). By simplification the two frequencies reduce to 212. and 211/.

I By way of example, the incoming signal of frequency a will be considered to-have the value 25000 and thelocaljfrequency n, a

value of 500. The in-put circuit of a second valve is tuned to substantially the frequency of theincoming signal, that is, in the neighborhood of 25000 cycles, and with this adjustment the local frequency of 500 will not get into. the i i-put circuit of the second'valve whenthe signal is not coming in. Hence the local frequency will be inaudible in the receiving device 19. WVhen the signal comes in, the current of the plate circuit of the first valve, having the two components will get across into the input circuit of the second valve as it will be of the order of the frequency to which the system. is adjusted or; tuned. -The two components referred to will have the frequency 25500, that is, (vii-n) and 24500, that is, (n-n) and current in the plate circuit-pfthe first valve will induce a current of similar components in the input circuit of the second valve. This in turn will produce a current in the output circuit of the second valve containing the receiver 19, having components of the frequency 50000 (2%) and 1000 (21%). A 50000'frequency cannot produce an audible tone in the receiver 19 whereas the 1000 frequency can do this. Hence, thelatter is heard by the operator. Since no current of audible frequency is induced in the secondary 14: when the signal is not coming in, that is, during the period of time between the dots and dashes, for instance, the receiver diaphragm will not be set in vibration. The dots and dashes there fore will alone produce vibration of the receiver diaphragm at a frequency of 1000 and the signals will be plainly heard by'the operator.

In the modification in Fig. 2 the local source of frequency is not a low frequency as in Fig. 1 but is a high frequency on which is superimposed a low frequency. In

neighborhood.

this figure as well as in the remaining figures the parts shown in Fig. l are given similar reference characters and a detailed description need not be repeated. The local source of frequency may consist of any desired de vice but I have illustrated by way of can ample an oscillating valve well known in the art. The plate circuit 322 of this valve is connected to the iii-put circuit of the first receiving valve by means of azprimary 23 of a transformer. A local source of E. M. F. 24: inducesa current by means of a transformer '25 in the grid circuit of the oscillating valve. .15. mathematicaltreatise of this embodiment wherein all of the frequencies are taken into account would be too involved for. this disclosure, and there:t'ore,*a consideration of the frequency of theincoming signal and the local. high frequency will be the only ones that will be essential. The low frequency a of the local source 24: will be consicered to alter or modulate the 'local high frequency n so" wherever the latter, or combinations of the latter with incoming signal is involved,it must be considered that the resulting components are modulated by the local low frequency a. I

lV'th thisunderstanding, the operation may'now be explained. a By way of example, thefrequency n of the incoming signal will be considered to have the value of 25000, the local high frequency a a value of 50.000 and the local low frequency a a-value of 500. The incoming signal, as before, gencrates an E. -M. F. in the secondary t in which is generated alo'cal E. M. F. having a frequency of 50000 (modulated or altered by the low frequency 500). Since the incoming ton signal generates an E. M. F. of 25000 cycles,

. in this same circuit there will'be produced in the plate circuit of the first valve a current having components with frequencies equal to the sums and differences of the said fre- 75000 (n-l-n), and 25000 (nyn), both-of which are modulated or changed by the local frequency 500. 3

The in-put circuit'of thetsecond valve tuned for the frequency of 25000 or in this This adjustment, therefore, will not permit passage of the component having the frequency of 7 5000, but will pass the frequency of 25000 which, of course, is i'nodulated. The 25000 cycles current will not in itself operate the diaphragm of receiver 19as it is entirely too high, but-the modulation of this frequency. by the low quencies. This will mean that the two components referred to have frequencies of frequency 500, will producean audible note in' the receiver, and this has been intensiiie by the local high frequency. 1 V

One distinct advantage of the system in "Fig. 2 over that'of Fig. fl is the amplification due to the combinationof-the local high frequency of 50000 with the incoming signal of 25000. By referring to the previous paragraph it will be seen that one of the frequencies of 25000 that passed into the input circuit of the second valve is due to the difference between thesignal n and the local high frequency 01.. This is the combination that gives marked amplification of the signal. This frequency of 25000 is the one that is modulated by the local 500 frequency to render it audible.

In Fig. 3 I have shown a modification of the arrangement of Fig. 2 wherein the battery of the plate circuit is displaced by a source of variable electro motive force such as an .alternating generator 26. By making the frequency of this generator of low value, say 500, for example, the local source 24 may be dispensed with. In other words, the

source 26 of Fig. 3 takes the place of both the. battery in the plate circuit and the generator 24 of Fig. 2. Obviously various forms of generators may be used in place of the alternator. The operatioi'r of this modification would be the same as, the sys tem in Fig.2.

.Referring to Fig. 4 the secondary 8 of the transformer in the in-put circuit of the valve a frequency of 50000 and a frequency of 505-00. The in-put circuit of the second valve may be tuned to pass 25000 cycles, or a frequency in this neighborhood. This will cut out all but the frequencies 25500 and 25000, both of which are combinations of the incoming signal with the local high frequency, consequently amplification may be made very great due to the amount of energy that can be put into the system by the local source. The out-put circuit of the second valve will have a current with components of the sum and difference of the frequencies of the in-put circuit, namely, 25500+25000 or 50500 and 2550-025000 or 500. The telephone receiver 19 will therefore vibrate at a frequency of 500 which will produce an audible note.

In the operation of the systems I have observed that the arrangement of Fig. 3 is most sensitive, that of Fig. 2 the next sensitive, and that of Fig. l the least sensitive when the incoming signal is weak. When, however, the incoming signals are moderate or of great intensity the systems in Fig. 1 and Fig. 2 have about equal sensitiveness and-produce greater movement of the diaphram than is the case with the systems of Fig. 3. However, I do not wish to state that this will always be the case, as under some circumstances it might be different.

I find that if the frequency of "the local source is exactly twice that of the incoming signal the operation is especially satisf-ad tory and the adjustments very simple, since in this case the in-put circuits of both valves are then tuned to the signal frequencies, one-' I of the new frequencies will be equal to the signal frequency.

I also find by actual test that the systems of Figs. 2 and 4, under most conditions, especially the latter, give excellent response,

are exceedingly sensitive, and show great,

ous other frequencies of signal and local source of energy may be used with like results when the adjustments are made in accordance with my explanation or equivalent thereto.

It will be apparent that various forms of generators may be used in-t'he place of those that I have described Without departing from the spirit of invention. Receiving devices other than the three element tube may also be used. As one example, I may cite the crystal detector, but I prefer the oscillating tubes on account of the ease of ad-.

justment and the superior results obtained.

While I believe the theory of operation to be correct I am not bound by it. I do know that the arrangement produces the results desired.

Having described my invention, what I claim is:

1. The method of receiving radio signals which consists in generating in a circuit an electro motive force of the signal frequency, generating in said circuit two local electro motive forces of frequencies differing widely from the signal frequencies and differing from each other by an audible frequency and causing a component of the current resulting from said electro motive forces to operate a re"eiving device.

2. The method of receiving radio signals which consists in generating in a circuit an electro motive force of the signal frequency, generating in said circuit-two local electro motive forces of frequencies differing widely from the signal frequency and difiering from each other by an audible frequency producing by said electro motive forces a current having a plurality of components, of frequencies that are integral combinations of the frequencies of said electro motive forces,

producing in a second circuit a current equivalent to atleast one of said components and operating a receiving-device by said component. 1: i I i 3. The method-of receiving signals which consists in generating a signal electromotive force, generating a second and a third electromotivc forcedilfering from eachother by a low frequency-and from the signal frequency by: a. high freeuiency combining all said electromotire forces'to create a first-and a second component having frequencies respectively equal to thedifference between'the fre uency of the si nal and that of each of theother said electromoiive forces, combinging said first andsecond components to produce a third component havin a frequen ey equal to the difference between the frequencies of said .fii'ctand second components, the frequency of the third-colnponent also being equal to the difference between the frequencies of said second and third electroinotive a low frequency an'dfromthr? signal frequency by a high frequency, combming all said electronioti've forces to create afirst and to said output circuit for indicating signals. I

a second component having frequencies respectively equal to the difference between the frequency of the signaland that of each of the other said eleetromotiye forces, combining said first and second components to produce a third component having a frequency equal to'the difference between the frequencies of said first and second components, the frequency of the third component also being equal to the difference between the frequencies of said second and third electromotive force and independent of the frequency of the signal, and indicating the sig nal by said third component. i

. 5. A receiv ng apparatuscomprising in combination an electronic relay having an input circuit and an output circuit, means whereby slgnallng oscillations are brought into said input circuit, local means for producing in said input circuit an electromotive force of a relatively high frequency as compared to that of the signaling oscillations. a vsecond local means connected to said input circuit and producing an electromotive force interacting therein with that produced by i said first local means, and means connected the R. A. VVEAGANTQ 

